Abstract
The aim of total hip replacement is to relieve pain and restore function in patients with arthritic hips. The majority of standard implants come with a variety of offset sizes based on anthropological data from cadaveric and radiological studies. The placement of these components depend on a number of factors including soft tissue tension and hip stability at the time of hip implantation. The depth of placement of femoral component is solely under the surgeon’s control and can be influenced by the presence or absence of a component collar and the level of the neck resection itself. Inaccuracies in depth of femoral component placement will lead to length inequality which themselves can cause patient dissatisfaction and complications. In order to accurately place the femoral component a sound understanding of proximal femoral geometry is important. An often used landmark in replacement surgery is the tip of greater trochanter which is said to be at the level of the centre of the femoral head. This study is designed to assess the accuracy of this statement in a population of patients presenting for total hip replacement surgery at Nottingham City Hospital.
Pre-operative and post-operative radiographs of the replaced and contralateral hips were obtained and measured. A line perpendicular to the axis of the shaft of the femur touching the tip of the trochanter was used as a reference for depth of placement of measurement. The centre of the femoral head was estimated using concentric circles and marked. The vertical distance between the centre of the femoral head and the reference line was measured; the distance was recorded with reference to the tip of trochanter. Similar measurements were made post-operatively to assess the accuracy of femoral component placement.
Pre-operatively the centre of head was below the tip of trochanter in 85% of patients. The mean distance was 10mmbelow the tip of trochanter, with a range of 6mm above to 24mm below. In only 15% cases was the centre of head at or above the tip of trochanter.
By contrast post-operatively 55% patients had a femoral head centre at or above the level of tip of trochanter. This, therefore, represents a significant degree of lengthening in all patients where the tip of trochanter was used as a reference point for femoral component placement.
These abstracts were prepared by Squadron Leader G. Pathak FRCS (Trauma & Orth). Correspondence should be addressed to him at Royal Hospital Haslar, Gosport, Hampshire PO12 2AA.
